Henderson Water Utility (HWU) retained Clark Dietz, Inc. to study options available for various improvements to the North Water Treatment Plant (NWTP). The NWTP consists of several treatment steps including a raw water intake, rapid mixing, upflow flocculation/clarification (superpulsator) units combined with lamella plate settlers, a contact basin, and filtration for treatment of Ohio River water.
The NWTP is designed for flows up to 12 mgd (million gallons per day). This flow rating is the result of the filter capacity. Each superpulsator clarifier is capable of treating 7 mgd for a total capacity of 14 mgd. Future construction of two additional filters could increase plant capacity to match the superpulsator capacity plus provide a safety factor of 2 mgd if that becomes necessary due to future demand growth. Construction of additional filters was not considered in the current project.
HWU provided Clark Dietz with an initial list of improvements being considered for the NWTP and these items were discussed during an initial site visit in September 2013. Possible improvements included:
- Replace the structurally unsound and leaking flash mixing basin
- Repair the leaking infrastructure in the northwest corner of the plant
- Replace the fine screen for easier removal of clam shells
- Develop an alternate method for the leaking contact basin bypass
- Install covers over the open water surfaces for algae control
- Replace the deteriorated wood baffles in the contact basin
- Rehabilitate or replace the corroded infrastructure
- Install VFDs for the high service pumps
- Replace check valves for simpler operation and maintenance
- Repair deteriorated and water damaged brick façade
- Replace windows, doors and brick exterior to improve aesthetics
- Update the main building HVAC to meet the recommended standards
Clark Dietz and HWU then completed a preliminary evaluation of these options, the goal of which was to prepare a planning level study in which alternatives would be evaluated based on operation & maintenance requirements and life cycle costs.
The improvements listed above include both imminently necessary modifications and those that are not critical at this time. With this in mind the improvements were divided among two phases. The following describes the pieces of these two phases and the reasoning behind their grouping.
The structurally unsound condition of the flash mixing basin drives the design and construction of Phase 1. The recommended solution is to construct a new flash mixing basin and drop box within the abandoned settled water aeration area to the west of the superpulsators. In addition, by constructing a new wall along the west end of the superpulsator clarifiers and a new effluent channel from the superpulsator clarifiers to the contact basin, the water leaking out and flowing beneath the riprap slopes on the west and north sides of the plant should be eliminated.
While constructing these improvements we will include other associated items such as replacing the influent screen, adding a bypass for the contact basin, replacing the deteriorated baffles and installing algae control covers. These improvements will be challenging to construct while keeping the plant in operation.
In addition, dewatering the unused areas of the basins and using algae control covers will result in less chlorine demand, improve plant operations and make maintenance easier. The costs for these improvements are summarized in this table.
Phase 1 Improvements Summary
|Replace Flash Mixing Basin and Drop Box||$ 570,000|
|Manually Raked Slanted Screen||60,000|
|Superpulsator Effluent Modifications||280,000|
|Contact Basin Bypass||120,000|
|Algae Control – Suspended and Floating Covers||100,000|
|Building Repairs – Critical||5,000|
The current schedule for this project is to take bids in the spring of 2015, with construction to start at the end of the summer (after high demand season has passed).